Field of the Invention
The invention relates to a method for the efficient utilisation of the hot air flows in a dryer system for goods to be dried, in particular for a vehicle painting plant, in which the waste air from the dryer is heated in a thermal post-combustion system and as clean gas is conducted as through circulating air recuperators, in which the circulating air extracted from the dryer is heated up and returned into the dryer.
Brief Discussion of the Related Art
In dyers for paint shops, in particular vehicle paint shops, the freshly painted goods to be dried according to the prior art, for example bodies, are mostly moved into the dryer on a support frame (SKID), the organic solvents being present in the fresh paint of the goods to be dried. Following the heating-up in the heating-up zone of the dryer, bodies for example enter the holding zone of the dryer at approximately 140° C.-180° C. Following this, the bodies leave the dryer.
The gaseous, organic substances liberated during the drying process are suctioned and fed as waste air (raw gas) to a thermal post-combustion system (TNV) for the oxidative conversion of the organic substances into the non-toxic compounds carbon dioxide and steam. Before entering the thermal post-combustion system, the waste air is regularly pre-heated in a waste air recuperator. The clean gas from the post-combustion plant initially cools down in the waste air recuperator and is subsequently utilised for heating the dryer.
This takes place in the manner that the clean gas is conducted further through circulating air recuperators which reheat the circulating air extracted from the dryer, following which the circulating air is again returned into the dryer. Finally, the clean gas can still be conducted through a fresh air recuperator in order to heat up the fresh air to be fed to the dryer.
This known drying process is no longer efficient enough because of the rising primary energy prices. The process heat requirement for the dryer and the real primary energy consumption are not balanced since the projected clean gas temperature of 160° C.-180° C. does not correspond to the real clean gas temperature. Experience has shown that the clean gas temperatures are mostly between 280° C.-320° C.
The aim therefore is to operate the thermal post-combustion system not at full load but at part load.